It is proposed to continue a research program designed to provide information about DNA base damage and its effects. The quantities and types of damage to thymine and adenine bases produced by ionizing radiation in vivo will be determined in bacterial strains selected for their known radiation sensitivities and for their genetically characterized ability to repair radiation damage. Specific products of base damage, such as thymine hydroperoxides, will be measured as a function of radiation dose, and time after irradiation during the period in which radiation damage is thought to be repaired. Since it has been found that undamaged base residues (bases, nucleosides, oligonucleotides) are released from DNA immediately after irradiation, these residues will be quantitated as a function of bacterial strain and postirradiation incubation time. The effect of O2 and several cis-platinum anti-tumor drugs on the quantities and types of DNA base damage as well as on base residue release will be determined. Radiation effects on carbon-13 enriched DNA in vivo and in vitro will be studied by NMR techniques. BIBLIOGRAPHIC REFERENCE: J. V. Paukstelis, E. F. Branagan, T. W. Whaley and J. D. Zimbrick, "Examination of DNA by 13-C-NMR," Abstract of paper to be presented at IVth International Symposium on Magnetic Resonance, Banff, Alberta, Canada, May 21-28, 1977. W. P. Unruh, J. D. Zimbrick and T. Gedayloo, "ENDOR Measurements of Proton Tunneling in 5-thymyl Radicals in Acidic Galsses," Abstract of paper presented at American Physical Society Meeting, San Diego, Calif., March 21-24, 1977.